Air conveyors such as that disclosed in U.S. Pat. No. 4,392,760 are well known and widely used in the art. Modifications and variations have been made to these prior art air conveyors in an effort to solve problems associated with conveying particular types of articles. For example, U.S. Pat. No. 4,822,214 discloses an air conveyor designed for conveying both PET container bodies and flat-bottomed base cups.
Prior art air conveyors, however, are not particularly well adapted either to convey relatively heavy articles, or to convey articles in environments where the conveyor may accumulate material forming a residue which increases sliding resistance between the conveyor and the articles. In order to convey relatively heavy articles, prior art air conveyors generally utilize relatively high air pressures which disadvantageously may transport articles at excessive speeds. Upon accumulation, articles transported at such excessive speeds may be damaged. Similarly, in order to convey articles which tend to stick to or otherwise generate relatively high sliding resistance with the transport surface, prior art air conveyors again generally utilize disadvantageously high air pressure. With heavy enough articles or large enough sliding resistances, prior art air conveyors are generally inefficient and eventually become inoperable.
It is known to provide curved transport surfaces with anti-friction ribs in dispatch tubes and protruding supporting elements in ski mats. U.S. Pat. No. 690,675 discloses a dispatch tube 1,2 having anti-friction ribs 6,7 therewithin. U.S. Pat. No. 3,473,483 discloses a preferably concave ski mat or track 10 including universal supporting elements 22 comprising spherical balls and means for rotatably mounting the balls.
Air cushion or flotation devices having various features for aiding to lift articles are also known and widely used. U.S. Pat. No. 4,805,626 discloses an air flotation patient bed including spheres 19 which prevent escape of air in chamber 25 unless bed 12 depresses spheres 19 within openings 21.
U.S. Pat. No. 3,692,192 discloses an air cushion lift pad comprising a flat base, a flat flexible diaphragm sheet and a flat cover plate provided with openings. The diaphragm portions exposed openings include perforations.
U.S. Pat. No. 4,355,940 discloses a platform 10 including a plurality of drive rollers 13 to transport loads. A plurality of air exit ports 14 are used to provide an air bearing surface for the loads.
U.S. Pat. No. 3,545,813 discloses an air-film conveying apparatus comprising a platform plate having holes 2 for passing compressed air from chamber 3. A protecting member 4 made of pile fabric is disposed on plate 1 to protect the flat bottom surface of transported articles.